Fragile sites are morphological alterations in the banding patterns of metaphase chromosomes that appear as non-staining gaps or breaks. Common fragile sites are induced by the DNA polymerase alpha inhibitor aphidicolin and appear to be ubiquitous in the human population. Comparison of known cancer chromosome breakpoints with the positions of known fragile sites has demonstrated a level of coincidence much greater than expected by chance, leading to the hypothesis that fragile sites may predispose to certain chromosome rearrangements in neoplasia. The position of the common fragile site at 3p14 coincides with one breakpoint of the constitutional translocation t(3;8)(p14.2;q24.1) in a renal cell carcinoma kindred as well as one deletion breakpoint in some small cell lung carcinomas. The t(3;8) rearrangement in the former case brings the 3p14 fragile site into close proximity to the c-myc oncogene on the derivative 3 chromosome. This project will investigate the 3p14 fragile site and the t(3;8) breakpoint by means of Southern blot analysis using a cloned c-myc DNA probe in conjunction with a new method for resolution of very large DNA fragments. The goal of this research will be to obtain a cloned DNA segment that carries all or part of the 3p14 fragile site and that may also carry sequences from the translocation breakpoint. These clones will provide the first opportunity to study a fragile site at the molecular level. They will be used to determine if nucleotide sequence homology exists between the 3pl fragile site and other fragile sites, for DNA sequence analysis to determine how fragile sites differ from normal DNA sequences, to determine the involvement to this site in other rearrangements and to investigate changes that occur when the site is induced with aphidicolin. The long term objective is to apply the method described in this proposal to additional fragile sites that may be involved in other cancer chromosome rearrangements.